ELY GREENSTONE. 145 



ancient volcanics of Great Britain." In some of the cases mentioned by 

 him, however, this clastic matrix is clearly of sedimentary origin, as lines 

 of sedimentation, with separation into the finer and coarser grained material, 

 are clearly recognized. In none of the numerous cases studied in the Lake 

 Superior region is there any indication that this clastic material is of 

 sedimentary origin, hence it has been concluded that it was due to 

 brecciation. The reservation must be made, however, that some of it may 

 well be a tuff deposit in which, as the result of the small amount that can 

 be studied, no differentiation in grain, etc., is shown. 



The mode of formation of these ellipsoids, as suggested, and the 

 preseiace in them of great quantities of amygdule;s, seem to point 

 conclusively to the fact that th.e lava in which they occur is a surface 

 flow, although the flows may have been of submarine formation. 



Ellipsoidal basalts identical in every way with those from Michigan, 

 whose charactei's have been already described, occur in the Vermilion 

 district of Minnesota, and are very widespread. An occurrence at one 

 locality was described several years ago by Winchell.* More recently, in 

 the last volume of the Minnesota report," a number of other localities in 

 the Vermilion district have been enumerated, in which rocks having this 

 structure occur. The greenstones possessing this structure have, however, 

 a much wider distribution in the Vermilion district than would be inferred 

 from the description given by the State geologist. Corresponding to their 

 wide distribution in the Vermilion district proper they have also been found 

 by reconnaissance to cover large areas in the adjacent portion of Canada 

 forming the continuation of this district. This distribution is practically 

 the same as that of the Ely greenstones, for this structure can be seen in 

 more or less perfect development on nearly all of the large exposures of 

 that rock. The accompanying illustration (PI. IV, A) shows nothing 

 essentially different from the sketches reproduced in Monograph XXXVI, 

 but is taken from a photograph and is, therefoi-e, of much greater value. 

 The photograph represents an exposure about 50 paces south of the county 

 road 1 mile east of Soudan, just northeast of Jasper Peak. 



The various observations recorded in Monograph XXXVI concerning 



a Ancient Volcanics of Great Britain, by Sir Archibald Geikie, Vol. I, 1898, pp. 184 and 193. 

 6 The Kawishiwin agglomerate at Ely, Minnesota: Am. Geologist, Vol. IX, 1892, pp. 359-368. 

 (■Geol. and Nat. Hist. Survey of Minnesota, Final Kept., Vol. IV, 1899, pp. 255-267, 274, 276. 



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